Can an ex-felon from the U.S. travel to Canada for vacation?

In general, and depending on the crime, no. However it's best to contact the nearest Canadian consulate or embassy and ask. If your conviction prevents you from entering Canada, you can apply for "deemed rehabilitation" basically you are applying to prove you are no longer involved in criminal activities. The conviction would have to me more than 10 years ago for you to apply for this exemption.