Is there anything else that I could use instead of it?
You could try Peychaud's Bitters (difficult to find), Fernet-Branca, orange bitters or other types of bitters. Worcestershire sauce may also be used as a substitute but works well in savory dishes. I wouldn't recommend it for a Manhattan.
Or, if you're very ambitious you can try to make your own bitters, although the ingredient list is somewhat intimidating! Good luck!
You can also order bitters from Amazon. I don't know for sure if they can ship them to Canada; try it and let us know. Fee Brothers is a very old company that makes some terrific varieties. I particularly like their grapefruit bitters.
@vecta has provided the canonical answer to which I agree.
Others provided alternate replies to the effect of have you tried this source, an example being Amazon.
Amazon Canada: ANGOSTURA Aromatic Bitters, 100 Milliliters.