Student or Learner
Is this sentence correct ?
Prices in the UK are high compared to / with / in comparison with those in Canada and Australia.
There are 5 million smokers in the UK, while only 2 million of those in Canada and 1 million in Australia.
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.
NOT A TEACHER
(1) Just a gentle reminder that some (repeat: some) people feel that there is a difference between "compare to" and "compare with."
(a) Mother: You are just like your brother.
Tom: No, I'm not. Stop comparing me to him. (= to liken. That is, to say that two things are the same. Remember that famous line from Shakespeare: "Shall I compare thee to a summer's day?")
(b) Father: I think that you should go to Harvard.
Daughter: Actually, I was thinking about Oxford.
Father: So what are you going to do?
Daughter: Well, I am going to compare Harvard with Oxford and then make a decision. (= consider the similarities and differences between two things.)
(2) As a non-teacher, I respectfully suggest that you consider using "compared with."