University of Toronto has an excellent graduate astrophysics program (totally biased answer because I'm in it, but we are basically the hub for astronomy in the country). Based on what I've seen though, I wouldn't do my undergrad at U of T. Like most big schools, the student experience sucks. Something to keep in mind when applying for university...the big name schools may have allure, but you'll just be a number to the administration, just another cog in the machine. You'll have to fend for yourself. Don't expect much one on one interaction or personal attention in any of your classes.
Only go into physics and/or astronomy if you are interested in the science and want to be a scientist. It's not the greatest means to an end for becoming an astronaut, as the two things are quite different from each other*. Of course, nobody makes career plans to become an astronaut, you need a plan B. What I'm saying is that if you really like the science, then physics/astronomy is fine as that plan B. Otherwise, maybe some other technical field, or even medicine would suffice. On that note, let's talk more about the requirements. If you're a Canadian citizen, you need to apply to the CSA's astronaut program, NOT NASA's. The CSA requires that you have:
at least a bachelor's degree in the natural sciences or engineering and several years of work experience (I believe it is 3 yrs)
OR
a medical degree and several years of work experience
OR
a graduate degree (master's or PhD) in which case no additional work experience is required. There may be a fourth option too, but I can't remember what it is (military?)
Don't quote me on this stuff, go to their website.
There was a recruitment drive this past summer, and I applied, even though I was not eligible, because for me it has always been a childhood dream to be an astronaut. I wasn't eligible because I just graduated with my bachelor's in Engineering Physics (no work experience) and just started my PhD in Astrophysics (no graduate degree yet). As a result, I was rejected. So, this recruitment drive came 5 years too early for me. But I figured, what the hell. I knew I was going to be rejected, but it couldn't hurt to apply. Who knows when the next recruitment drive will be.
The *manned* space program is definitely not that relevant to science (although people do debate this, especially when it comes to the exploration of Mars). I think a lot of people are of the opinion that robotic exploration is more efficient, we will learn more from it, and carries less inherent risk. Besides, when it comes to the study of anything beyond our solar system, the word "exploration" is no longer quite right, regardless of whether it involves humans or robots, because we will not actually be going there. For the rest of astronomy, what's needed is the next generation of orbiting observatories (i.e. space telescopes), and that is being worked on as we speak. So, to answer your final question, we don't really *need* to send people to space...that is the wrong question to ask. We do it because we *can.* So the question to ask is whether our policymakers will continue to think that it is worthwhile to send people into space. Nobody can predict that. I've heard that the U.S. congress is quite fickle about the space program, and we are falling on hard economic times. If those economic hard times become a more permanent fixture and are just a fact of life, then it will be even more difficult to economically justify the manned space program than it is right now. So, nobody knows what's going to happen. That's the other reason why you don't *plan* to be an astronaut (the first reason being the low probability of being accepted). ;-)