Canada has been tightening up on this sort of thing recently - it's always been the case that a criminal conviction debars you from visiting but they've rarely actually bothered to ask or check.
They do seem (read in another newsgroup) to have a lot of data on US convictions - what they have on UK ones, if anything, I've no idea.
Unlike the USA it has to have been an actual conviction - just an arrest doesn't count - and they do have the concept of rehabilitation - 5 years for a minor offence, 10 for a more serious one.
http://www.cic.gc.ca/english/visit/conviction. html#deemed
has some interesting info.
As Jimjools says, I don't think they routinely ask about this sort of thing, particularly on a short holiday visit.