From around 1983 through 1988, Marvel and DC re-priced some of their comic books for the Canadian market.
Most Marvel comics published during this period either had US cents prices only, or US, Canadian and UK prices all together on the front, something like this:
The prices on the covers of Canadian price variants are always higher than the standard price on the cover of US issues.
You can also tell Canadian issues, because they always have a bar code (UPC) at bottom left of the front cover rather than Spidey's head.
There are plenty of US editions which have bar code UPCs at bottom left as well. These are also a much-collected niche (known in the hobby as newsstand variants).
Canadian price variants of DC Comics have different (higher) prices than their US edition versions of the exact same issue #s. The word CANADIAN is also printed below the price, sometimes. (But not always!)
Here is Batman #357 to illustrate this.
There are hundreds of Canadian price variants, but keys are the way to go.
Here are some ideas for you to look out for.
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Most valuable comic books of the Copper Age (1980s)
Full Canadian Price Variants Comic Book Price Guide