Bus ads aren't a big deal, so chill and enjoy your life

I'm not going to get into any sort of is there or isn't there a god debate. I'm not religious, and that's a personal decision. There are many, probably too many, religious out there, and most of them believe in a different god, and if it makes you happy to believe that your god is the only "real" one, or if you want to believe that there is a universe full of diverse gods, or if you think it's all bullshit, then more power to you. It's your business.
But if I've learned anything in my career in newspapers, and I hope that I have at least learned a thing or two so far, it's that you have some cash, you pretty much buy advertising space for anything. You want to hook up with a transvestite midget, buy an ad. You want to sell extra book shelves you don't have room for, buy an ad. You want to find a good room in an inexpensive, though maybe slightly cult-ish, home for your senile parent, buy an ad.
And, of course, if you want to tell everyone to relax because, hey, there probably isn't a god, buy an ad.
If the City of Ottawa does, and they likely will, decide to allow ads by an atheist group that says something like, "there probably isn't a god, so relax and enjoy your day", they will be making the right decision. Sure, the ad is probably expensive as hell and will be rather large, they aren't advertising anything illegal or immoral.
If a religious group feels like buying a bunch of ads that says "god loves you", go ahead. Regardless of what an ad says doesn't mean it's true, whatever the message is. For the religious folk that want to spend their time protesting this, they may want to ask themselves the question of how strong their faith really is. If you are a true believer, an ad that says there isn't a god shouldn't make you feel differently. To these people I say stop worrying about what other people will think when they see these ads. It's their business, and their beliefs are just as a valuable as yours. So relax and enjoy your day, however you want to do that. There are bigger fish to fry.