The biggest problem with fleeing to Canada, who is relatively good about accepting refugees, is they would likely be next. Global warming will be making a large swath of the USA less habitable plus it is always a good distraction to have someone else to loot. Once the US government is fully fascist, then there is no moral issues (from their point) of invading Canada for resources and fresh water. Plans have been forwarded since the 1950s, seeking to export Canadian water south*. Much safer than attacking Russia or China and it creates a outlet for all the arms the US manufactures.

https://en.wikipedia.org/wiki/Water_export