Hello and welcome.

When it comes to "coins that don't look like normal coins", there are two basic explanations:
- Mint error - something went wrong when the coin was made.
- Damage - also known as "post-mint damage", this is when something or someone either deliberately or accidentally damaged the coin, long after it left the mint.
The first explanation creates valuable coins, the second explanation does not. And it's sometimes not easy to tell the difference, especially for inexperienced collectors.
Regarding your Canadian dollar: it would probably be best if you started a new thread, in the
Canadian Varieties and Errors subfourm, with larger pictures of both sides of your coin. But just from what I can see on this smaller picture in this thread, it does appear to be damage, rather than a mint error. The "second strike" is incuse, judging by the dimples, so it was not formed by a coin press striking a coin twice (which causes a genuine double-struck mint error), but formed by squeezing a second normal coin onto this coin in a vise or similar arrangement, so that the design from the second coin pressed into this coin. It isn't really possible for such a thing to happen while a coin is being made. But I'd really want to see clearer pics of both sides to be sure.
As for the reason why it's there in your safe... well, sometimes people keep odd-looking things whether or not they are valuable. Or they might be mistakenly thinking its valuable, when it isn't. If the person who put it there is no longer around to ask, and they left no notes in the safe explaining themselves, then we'll never know.
Don't say "infinitely" when you mean "very"; otherwise, you'll have no word left when you want to talk about something really infinite. - C. S. Lewis