One thing you should definitely try to do is research! Do you have credit room in your degree program to complete a senior thesis, independent study, or even assist a graduate student with their research? You don't necessarily have to publish anything, but getting your foot in the door will be both informative for you and smiled upon by an adcomm!
Another thing to consider is what subfields you're interested in. I would personally advise you to try as many different areas as possible as you fulfill credit requirements, but consider taking upper level courses in the subfields that interest you the most.
Lastly, it is never too early to begin preparation for your application. I'm not sure if Canadian schools require the GRE or other testing systems, but if so, studying in your junior spring is advisable as it leaves ample time for potential retakes. You can also start researching institutions and faculty members with whom you would like to study!
And of course, keep those grades up! It depends on the school, but consider a decent absolute cut-off to be a 3.5, with a greater likelihood of acceptance in the 3.8-3.9 range.
Best of luck!