It's definitely a balancing act, but doable all the same. I was able to complete the week end warrior QL2 during 1st year university. It wasn't easy, but having taught the new reserve BMQ, I know it is less demanding and shorter than the old QL2. Once you find your comfort level, you will know when you have to take a night off work to study or a week end off training to complete training. Every unit I've been involved with has placed the importance of school VERY high... it's the new army afterall. Reserve units are generally very supportive to soldiers who have to take a night or 2 off (make sure you know the minimum requirements to avoid trouble). I've had good experiences dealing with my profs at university (extensions if needed or missing a class for an exercise or parade), but I've heard horror stories about prof's being jerks - so that is definitely a wildcard and school/prof dependant (ie: out of the military's control).
If you can't handle the pressure and can't make the commitment at first, you can always go on an education leave for a couple of months to get yourself settled in school, then go right back to the reserves (called ED&T leave).
From my experiences, I was able to juggle it all, get a couple of degrees, go on ED&T for 4 months to complete an international work-term, go on a few ex's and even doing a rappel master course during the university term. MOST IMPORTANTLY, I was able to fund my 7yr university career with THE BEST PART TIME JOB IN CANADA. I just can't write that large enough. It also set me up nicely for a career in the regs (experience, pension, higher pay incentive, etc).