We have not heard of/from Canadians credit being affected by defaulting on U.S. credit. Not that it couldn't happen if some credit issuing entity wanted to put forth the effort and expense to bring suit, but for a timeshare there probably isn't enough money for them to put much into the little reward they could get when they can just foreclose and sell the TS to someone else.
You can, however, count on getting letters and phone calls and emails promising (threatening?) to turn you over to collection and never being able to use their facility. Feel free to demand in writing that ALL correspondence be via USPS, and block phone calls/emails. Also change any credit cards they might be able to access.
Having a credit default will have zero effect on your ability to travel to the US or anywhere else. I'd go so far as to say that you could default and then buy another TS on your next trip to the US or Mexico!
Jim