hey frozen-fire,
I bought a canoe 3 years ago and just recently invested in my first boat so I can give you some advices on this . Here's a few things that comes to mind:
1) Length-wise, I think a 15-16' would do just fine for two people
2) Although you guys prefer paddling at the mean time, I'd say try to get one with a motor mount or a square stern one. Sooner or later you might want to explore further away from your launching point or you might want to start trolling, it's alot easier to do it with a trolling motor/small gas motor, I'd advice you to keep that option open even if you won't be getting the motor now.
3) Keep the weight of the canoe in mind, seeing how you and ur girlfriend combine to be around 250lbs, I'd assume that you're 150lbs, it might be difficult for you to lift it onto the top of your car. (I'm guessing your girlfriend won't be able to help much here) I own a 16' fiberglass canoe and it weighs almost 80lbs, I can't load it on my nissan sentra on my own. (although i am only 135lbs but i'm not that weak neither )
4) For anchoring, I have been using a juice jar filled with sand, it works fine when it isn't too windy (15km/h or less), however when it's too windy out it wouldn't be safe to go out on the canoe anyway. Lots of people are using drift sock and they swear by it, I haven't used one so far.
5) Car mounts: Canadian Tire has those styrofoam mounts and it's been working fine for me, probably not worth getting rack installed onto your car when you're only looking at spending $250 or so for the canoe.
6) Check kijiji/craiglist/buysell, they sometimes have good reliable canoe for that price. Just for a reference I bought mine that comes with a 1968 1.5hp motor (with minor problems) for $350. Mine is quite old though, but reliable.
7) I have seen Civics tow trailer/boats, although it's not designed for that purpose but I believe they do have a towing capacity. By upgrading breaks/transmission fluid (i'm not sure what you need to change here), you can probably get away with towing a 12' tinny with a small outboard. I have seen them go as low as $400 for a used package.
8) Don't forget that you'll need all the safety equipment, i.e. PFDs, paddles, safety kit (with ropes, whistle, flashlight, etc)
That should have taken you a while to read lol ... and is all i could think of for now, if you need more help. Feel free to PM me.