Chances of getting admitted to USA universities for Fall 2021 As I see, a lot of students have already deferred their Fall 2020 applications to Fall 2021 next year due to Covid 19.
In this scenario, does this mean that, the fresh applicants for Fall 2021 will have to compete to with more number of applicants and less number of available seats?
In this case, will Canada or Europe be a better option, because there should be some guarantee to get an admit, and this guarantee is much less for USA?
With the fear of not getting admitted and a heavy application fee in US dollars is already intimidating.
This is going to depend on your field, and the schools that you apply to and what their individual situation is, among other factors.  As someone in the US, that's also not to say that things won't be competitive in Canada or Europe either, as there are Canadian universities, as well as possibly European universities, that are just as reputed as some of the top universities in the US (at least as far as what I know in my field), so it's a flawed assumption, at best, to assume you'll be admitted to a program if you apply to Canadian/European universities.
The only advice I can give would be to contact the programs you are interested in and ask what their situation would be for the upcoming admissions cycle and if you're better off applying in a future cycle.  What I will say is that graduate admissions is generally competitive and a crapshoot no matter what the timing is.  Therefore, if you want to apply to US universities, and see where you get lucky/hope for the best, since the worst they can do is say no.