The European and North American migrating birds are two different populations. If it comes here it will come through human transmission, not from birds.
"...not from birds."
probably not - although i think the Arctic Tern runs a course up the eastern U.S. seaboard and down the European/Africa coast on its migration?
And what about bird imports - or bird products. Can a dead and processed bird carry the flu?
I believe there isn't much migration from northern Europe and Asia to North America but there may be some. But, as this q&a points out, some type of transport of birds or human activity, as you say, are much more likely to bring in the influenza:
Q. What is the likelihood that avian influenza will jump the Atlantic to North America?
A. Migration routes tend to be north-south, so there is not a lot of bird traffic from Europe and Asia to North America.
The greatest risk of H5N1 spreading from Asia to Canada is through human activity: travel, illegal transportation of infected birds and movement of poultry products.
West Nile virus, for example, is believed to have come to North America in ducks imported from Israel. However, there is virtually no legal importation of poultry from Asia or Europe.
Dr. Éva Nagy, a virologist at the Ontario Veterinary College in Guelph, Ont., said the risk of avian influenza comes from individual travellers, not poultry or migratory birds, and it is essential that travellers who come into contact with poultry abroad stay away from Canadian farms for at least two weeks. "When you return to Canada and fill out a customs form, it's really important to tell the truth when answering the question about visiting a farm," she said.
http://www.theglobeandmail.com/servlet/story/LAC.20051014.FLUSIDE14/TPStory
I would add that bird stowaways on freighters and other vessels are not at all uncommon.
Not true. Birds migrate from Siberia/russia over the Bearing Strait into Alaska and Canada. These birds then move from Canada into the Lower 48 states. Along several pathways. The largest being the Miss. Pathway that includes 12 states.