Hi
As long as you meet the citizenship residency requirements, you can apply. You have to be ready to fly back to Canada on short notice when they want you to appear for your exam and later for oath. You might have 2 weeks notice to go. They do not let you schedule these things at your convenience and it is a hassle if you postpone.
No, you have to be resident in Canada on the date that you apply. You can leave after you apply.