The only way I could get from DCA to MSP for LH miles on the day I wanted is in AC business class with 85 minutes connection in YYZ.
I realise this means going through both Canada and US immigration.
I will have carry-on luggage only, so no checked bags, and am LH Senator (Star Gold) with an EU passport and both ESTA and advance CBSA, but no Global Entry or Nexus.
Grateful for views on whether this 85 minutes connection is doable.

Is this AC to AC or is one of the legs on UA? If it's AC to AC it violates cabotage and isn't allowed.

It is AC to AC but LH booked it as two separate flights, probably because of the cabotage issue..
I have checked my booking on the AC site and it is also showing as two separate flights.
I will have no checked bags and two separate boarding passes, so maybe it will be OK.

This will be tight. You might be able to avoid CBSA (Canada border control) and head straight to US security and CBP based on your second boarding pass, which would save some time, but there can be big lines for both of these depending on the time of day.

Thanks, it does seem risky.
I may decide to leave Washington for another day and come directly to YYZ from Europe as there is still availability in J for miles. No problem with onward flights in J on AC to final destination MSP as it is international while UA only offers basic Y on domestic flights for LH biz mileage tickets.

I’m assuming by two separate flights you mean two separate PNRs? Regardless of that though if AC flags this they may not let you board to next flight as *THEY* are the ones that get in trouble for cabotage issues. AC deems anything under 4 hours as cabotage.

Probably due to an interpretation of what constitutes cabotage by U.S. Customs (or whoever the enforcer is). Posted an example in the cruise forum about the PVSA a few months ago. US Customs states that booking a cruise from say S.F. to Vancouver on a cruise ship, and immediately getting on the next cruise on the same cruise ship from Vancouver to Seattle is a violation of the PVSA.

https://www.flyertalk.com/forum/35150308-post7.html

Interesting.

So if it's over 4 hours it's not cabotage?

Anything over a 4 hr layover as far as flights within North America is consider a stop instead of a layover (at least if there is a legal connecting flight within that time).

Many thanks to all for the interesting comments and advice.

It is on one PNR as part of a round trip miles ticket from Europe to MSP.
The risk of AC and/or US customs stopping me boarding combined with the tight connection has persuaded me to rebook on a direct LO flight WAW-YYZ, with the added benefit of saving around $200 in charges.

Cabotage is indeed sometimes overlooked as a potential problem, both for the transport of goods and in this case passengers.

AC has terrible on time record (something around 50% of the flights are delayed), and these short haul flights the most impacted. I would not attempt this itinerary unless you are ready to spend the night in Toronto.

Thanks - your advice has definitely made me change my mind!

Done US to YYZ to US itinerary on AC before. AC will only issue ticket if the connection is more than 4 hours.