Nothing. OP seems to be fishing for something and not providing information. That's really suspicious for a first-time poster.

OP - To answer your question, any UA agent can theoretically rebook you on any carrier, including one which actually requires UA to purchase a ticket for cash, e.g. WN. The agent's position (supervisor) may make a difference.

Whether and under what circumstances that happens or not, is entirely dependent on the specific set of facts. Bottom line is that many factors will come into play, you haven't told us what those are and thus nobody here can give you an informed judgment.

Yeah, but practically, will they prefer to rebook you on a AC flight or will they prefer to give vouchers?

What does "next flight available" means on United Airlines?
 

Sorry I must have read only the first lines ... UA agents at the airport can book - on their own - any UA flights (code share or not)
As for the others airlines , partner or not , they will need to contact the airline and endorse the ticket , according to what I know they will normally offer only UA plate and code share , unless you ask specifically or if you have high status , they will tell you to take the flight the next day (cheaper for the airline).
Again - you said at fault - what happened ? What did they do with the rest of the passengers as I assume you couldn't be the one and only traveler affected by it ..

Yes, BUR-YVR. 35 min stop in SFO (it is a legal connection!). First plane arrived late, didn't make it to the second one. And yes, I was the only one on that plane doing the BUR-YVR trip.

Thank you ReduceTC!

I'm not sure what you mean "ua member", though I resent the tone. People here are trying to be helpful. If you don't like their responses, just ignore instead of hostilely criticizing them.
If you are asking whether I am a member of United Mileage Plus, though it's irrelevant, I am. I formerly had elite status, and I've missed connections on United.

You missed connections on United and you were rebooked, right?

What does "next flight available" means on United Airlines?
 

In my experience, United agents definitely have the capabilities to rebook you on any airline, especially, if its was the airline's fault.

I once missed a connection (last flight out) and was rebooked on AA. Doesn't happen often, but I think it all depends on your status and the cost it would incur to the airlines.

Hotel and meal vouchers will usually be the more economical method for airlines as they have contracts in place, and certainly, having you back on their next available seat would be no additional skin off their back.

Don't they have contracts in place with their codeshare partners also?

emilio911, welcome to FlyerTalk!

I've been a 1K elite on UA for the past 18 years, have lived within 15 mins. of SFO for over the past 30 years and there is an important piece of information that is not clear from your account. That concerns the reason why your first flight (from BUR to SFO) was late.

If your first flight was late due to weather or air traffic control reasons, those are not considered reasons chargeable to United, even if your connection time at SFO was within a legal time. United may still be willing to put you on the AC flight to YVR, but it is not required to do so. If the reason for the late arrival of the BUR to SFO flight was truly chargeable to United -- that is it was a mechanical problem with that aircraft, a late arrival of crew or other reasons which make United responsible, it will be required to use best efforts to find alternate, available transportation that day.

Because SFO is well known among UA elites for having many weather and ATC delays, those travelers who know about SFO's reputation and are making important connections, would rarely, if ever, accept a flight schedule with only a bare minimum connection time at that airport.

Whether or not the reason for the "misconnect" is chargeable to United or not, a misconnect is still a misconnect; and, as was correctly pointed out above, the solution to the misconnect will depend on the workload and willingness of the UA agent, and his/her experience with AC's accommodation capacity and system.

A 35 minute connection BUR to YVR on UA metal is not going to work most of the time. T1 to T3 connection.

Thank you for your answer Ocn Vw 1K,

Don't you think UA has direct access to the AC system since the AC operated flights are codeshared with UA?

I had a very similar situation earlier this month... UA flights booked YYZ-IAD-LAS. The inbound flight into YYZ went MX and was delayed for 4 1/2 hours, which of course would have caused me to miss my connection. I called the UA phone agent and eventually (after he got the AC people on another line), they confirmed me onto the AC YYZ-LAS non-stop flight the next morning along with the hotel in Toronto and meal vouchers, since it was impossible to get any other flights in to LAS the same evening (and that included other AC routings via DEN or SFO).

So yes, when it is something that is under THEIR control (such as MX), they will most certainly do what they can to get you to your destination, but you should also definitely have in mind the specific flights to recommend to them.

UA might have direct access to AC's inventory but there might be issues with ensuring that the booking is accepted by AC. This issue arises repeatedly with members of United's MileagePlus program booking segments on one reservation with United and other Star Alliance members, esp, on award travel. That is why UA may have to phone AC or other *A carriers in order to ensure the booking, just as reported above by YOWTraveller.

Dealing with the world's largest airline, and one that is still in the throes of a poorly executed merger, one's personal experience is usually not sufficient to predict what may happen in future travel scenarios. That's why FT is such a valuable resource - it allows us to share experience, and exchange tips and strategies for dealing with the vagaries that come with flying the 'friendly skies'!

Your certainty that phone agents cannot rebook you onto a *A carrier is misguided. I've had this happen, more than once, during IRROPS. If you get the right agent, and behave the right way, magic can happen over the phone line while the masses are waiting in an hour long queue for in person assistance.

Bon chance!

Yeah OP is clearly just wrong on this point. We're still missing a key piece of information here, which is what was the cause of the inbound delay? If it was ATC (very likely given we're talking UAX into SFO), UA is not going to rebook him on another carrier unless he's GS or, maybe, 1K.