I would not really even consider them to be the same type of tool frankly.
Canva is like a design crutch tool. I feel like it's more meant for helping people hack together bits from templates for the severely artistically challenged. (Yes, artistically gifted folks have done amazing things with it.)
Actual alternatives to photoshop are things like paint.net (fucking love it, honestly unless you are an actual artist it can do everything you actually need to do, much easier than photoshop and it's free) and the gimp (don't love it but it's a very powerful tool, the issue is it has a steep learning curve like photoshop, however it is free and powerful as fuck.)