Sure, but having a smoking section in Tim Hortons isn't going to change that. I'd think it'd make it more likely for smokers to throw their butts out in a manner that can be properly disposed of, rather than making them smoke outside.
Note that I'm not advocating smoking or smoking sections. Smoking is awful on many levels and I'd rather see it go away entirely. I'm just pointing out that it's ridiculous to say having a smoking section in Tim Hortons is going to have a significant impact on the environment. Jumping to "this is going to fuck the planet" is crying wolf, it's going to result in people either getting sick of environmentalism or more subtly problematic it'll result in people thinking they're making a difference when they're not. The plastic straw ban, for example. Plastic straws were never a major contributor to ocean plastic waste. By far the largest contributor to ocean plastic waste is discarded fishing equipment, but I don't see any campaigning to reduce seafood consumption. People banned straws instead and then thought they'd accomplished something.