I wouldn’t like it… but… there may conceivably be morally justified reasons for Americans to do so.
For instance during 9/11 all flights over the US were rerouted to Canada and we sheltered thousands of Americans.
Perhaps if there was a huge drought in the US populations might be dying of thirst and may want to relocate north. Should we say Yes, or No? It would change us, affect us, and cost us, but could we really say “No?”
BTW we have 7 Wal-Marts, 32 SEARS outlets, 47 McDonalds, 6 Burger Kings, 3 Old Navy stores, 7 GAP stores, (and 4 Target stores being built) in Calgary already, 60,000 American citizens, and the Ford F150 is the most numerous vehicle in the province so you would feel right at home.