errr... Am I missing something? It seems the OP is solely worried about price, not miles. If the price difference is enough to justify traveling to LGA why the return to YUL? There's no way this is the cheapest option from LGA to LAS, or is the OP expecting to skip the LGA segments and be able to fly the rest of the itinerary?

Well this one that I booked last week was 200 cheaper than anything direct yul-las or lga-las, or with the original point of my OP, that for my next summer vacation, LGA-YUL-Anywhere fun, I'm finding fares to all over the map that are 500-1500$ cheaper than direct flights from either YUL or LGA/ORD/BOS

I share Aliquot's befuddlement. Even this far in advance, I'm seeing new york to LAS during Quebec's "construction holiday" on united.ca at $254 ai one way, returning LAS-YUL on AC one way at $272, for a total of $526 including all extras. If you're finding that for $500 cheaper, tell me how!

...

As I was saying to Aliquot LAS is in 3 weeks and *220*, not 500. AC from YUL is 800+ whereas I paid 603 on expedia

In my *OP* (that you didn't read apparently), I mentionned finding fares to europe and SYD for 500 to 1500 cheaper, as in LGA-YYZ-YVR-SYF for 1735 vs 3000 for YUL and various amount for LHR, CDG, MAD, TXL, MUC etc... for anything from 500 to 1100 cheaper and in fact, most of the times I could get paid Z from LGA for cheaper than cattle from YUL

In the OP's defense in the past I have been able to book cabotage style tickets on the AC website (AC stock on all AC metal). One time, when I checked in at the UA operated counter for the first segment back to YYZ, he gave me a very long talk about how my ticket was illegal and yada yada yada... so he refused to print out any BP's after YYZ (I was on a MDT YYZ YVR HNL ticket)... so knowing not to aggravate the situation, I knew I could simply have my BP's printed at YYZ T2 MLL (yes, this was when AC domestic was out of T2!) which I did without problem. Now, if I had known about FT at the time, I might have balked at confirming this ticket online, but I was a relative noob back then too!

So when it came down to it, I successfully booked and flew a cabotage ticket!

I'm still confused. I understand you will save money flying from LGA, but why are you backtracking to YUL? $603 is an extremely high price to pay NYC to LAS three weeks in advance. For 3 weeks from today there are fares starting at $314 from LGA or $524 from YUL. As it sounds like price is your motivating factor I'm befuddled.

But yes, I'm not sure about the legalities but it is certainly possible to buy a ticket through Canada to and from the U.S. I have done ELP-PHX-LAX-YVR-ANC-FAI.