I'm going to apologize in advance because I really don't have any details and this is just a bit of a stab in the dark.
It was a children's or young-adult fiction novel that I read approximately 15-20 years ago in Canada.
I think there was a young boy and he collected stamps (or coins?) and he found a stamp which was a duplicate of another he had. However, there was one difference: there was a man or person in one that wasn't in the other. I vaguely remember a boat or ship that resembled the "Bluenose", but it could have been older like from the colonial era. I'm not sure if it involved time travel, but I'm pretty sure he basically got sucked into another world; the world of the stamp/coin.
Sorry for the vague and small amount of details... If anyone has any ideas of what it might be, I'd be eternally grateful; it's been bothering me for weeks!