I don't know if it's "normal" but it certainly did happen. Perhaps the job opportunities were better in BC (more building taking place) so that drew him back to Canada. With Seattle and Vancouver being so close together, I think there was a lot of back and forth.
In the early 1900s, my grandfather used to regularly go back and forth between the 2 countries. He told my sister once that when things "dried up" in Canada, he would head to the US and liked to work in saloons and travel around. I think I've found him on the 1900 US Census working as a barman in a saloon in Oregon, but he's back with his family in Saskatchewan for the 1901 Canada Census. By sheer coincidence, I found the marriage of this grandfather to my grandmother (an emigrant from the UK) in Spokane, Washington in 1913, but they are in Lytton, BC, for my father's birth in 1914 and back to Saskatchewan by the 1920s. He was a carpenter so could pick up jobs in that trade. He was a bit of a wanderer in his younger years.
I don't think we know if Harry ever did get naturalized in the US....the documents were an intention of naturalization. I just looked at the 1910 US Census again and see that the Harry Foster rooming with the Kendalls is shown as being born in Sweden as were his parents

I think it is far too coincidental for this not to be the "Harry Foster" who marries Minnie. I am anxious to check the marriage registration now to see what the POB states on there. Perhaps, Harry was a bit of a story-teller!!
Susan