Do people really watch the NHL in June? Sure, if the Jets were in the Stanley Cup it'd be nuts, but who cares if the Lightning are playing the Golden Knights or whatever. Suppose the CFL season moves back three weeks, and the Grey Cup is the first weekend in November. Doesn't that mean there's only one potential week of overlap, which, in all likelihood, translates into one, maybe two CFL games? I can't see that being such a big issue.
That said, I'm pretty impartial one way or the other. If the Grey Cup is in Winnipeg in November, I'll go, and not care too much about the weather. It is disappointing how the attendance drops with the temperature, however, and if there were a way to mitigate that a bit, I'd be for it.