Former landscaper, if anyone's interested in an easier, cheaper way that won't poison the land, your family, and any nearby streams....
It's hard to start over on a lawn once the grass has started growing. Tilling or harrowing a growing field of grass this time of year will be a lot of work, will turn over a gazillion weed seeds that will grow with wild abandon and outcompete your grass. And the result will be very lumpy and bumpy. But a good way to start now, is to simply mow it regularly (4-5") through the growing season with mulching blades or a flail mower so all the little grass bits go back to the soil. That way, you'll have already improved your soil and knocked back the weeds some before you plant your seed.
Once everything dies back for the winter, cut everything pretty short one last time and apply organic fertilizer like Milorganite or compost. Frost/thaw will work it into the soil. Then depending on your climate (I'm not familiar w/ Canada zones) either in late fall or early spring, when the ground is mostly bare, smooth out your rough areas and lightly scratch the rest. Put down Contractor's Mix grass seed per label directions; the fast-growing rye in the mix will outcompete weeds while the fescues gets a start. You won't have to worry about enough moisture these times of year. Then once your grass is up, just mow regularly. If you need perfection, spot-treat any weeds.
If your soil is poor, reapply the organic fertilizer every year. If your soil is very poor, apply some now, then in late fall.
Organic fertilizer will improve your soil condition, making it more favorable to grass and less hospitable to weeds, and the effects are permanent. Chemical fertilizer is a quick one-shot deal that also boosts weed growth and does nothing to improve the texture, pH, etc., of your soil. Organic fertilizer is also cheaper.
Folks seem to think organic fertilizer takes a long time to work, but you'd be surprised how fast it works. You can go from red clay to earthworms in a year.
Glycophosphate will kill any grass--permanently--and knock back most weeds--temporarily. Aside from the dangers, it really doesn't work that well.
(I realize I'm probably never going to get any converts to my natural methods without pictures, so maybe I'll work on that. Give me something to do while I wait for my tractor to arrive.