In a average American box of nickels or dimes, 5-10 Canadian ones. But I also have crossed the border (Detroit/Windsor) to buy Canadian coins. I am planning to go again before the end of the year. I was considering buying them but I will keep on searching!
Interestingly in US coin boxes I found the following Canadian coins
1933 & 1941-present, one cent
1937 and 1941 nickels both in XF condition
1946, 1949, 1953, 1962, 1964 and 1966 dimes
but no quarters older than 1969