It has been estimated that about 24% of all active duty military
personnel served in Viet Nam between 1964 and 1975. To add further
perspective consider the below information on draft dodgers and
deserters who fled to Canada.

http://www.cic.gc.ca/english/departm....html#chap6-14

From the above URL

Draft-age Americans in Canada

"American draft-dodgers and military deserters who sought refuge in
Canada during the Vietnam War would ignite even more controversy, some
of it provoked by the Canadian government's initial refusal to admit
those who could not prove that they had been discharged from military
service (this changed in 1968). Draft-dodgers were usually
college-educated sons of the middle class who could no longer defer
induction into the Selective Service System; deserters, on the other
hand, were predominantly sons of the lower-income and working classes
who had been inducted into the armed services directly from high
school or who had volunteered, hoping to obtain a skill and broaden
their limited horizons."

"Starting in 1965, Canada became a choice haven for American
draft-dodgers and deserters. Because they were not formally classified
as refugees but were admitted as immigrants, there is no official
estimate of how many draft-dodgers and deserters were admitted to
Canada during the Vietnam War. One informed estimate puts their number
between 30,000 and 40,000. Whether or not this estimate is accurate,
the fact remains that immigration from the United States was high as
long as the war raged and that in 1971 and 1972 Canada received more
immigrants from the United States than from any other country.
Although some of these transplanted Americans returned home after the
Vietnam War, most of them put down roots in Canada, making up the
largest, best-educated group this country had ever received."

Gene Myers