Best way to get a canal tour?

I don't have a specific company recommendation. The place we stayed said they were pretty much all the same. . . I would have to guess some are better than others. I would say to make sure the boat is completely open air or all windows are open. It was threatening rain the day we needed to go so the glass roof was up. It obstructed views and pictures.

we used the Blue Boat company - some prefer Those Dam Boat guys.
But the Blue Boat does have a glass roof enclosure.
We got our reservations ahead of time on line and showed up at the specified time - did this about 2 weeks before we left.
Have fun!

will you be OK if you have paid ahead and it is raining or stormy at the time you reserve?

We took 2 canal boat tours a few years back and could not really distinguish one from the other. Then, a few years ago, upon leaving Our Lord In the Attic church in the red light district, we went over to a group of taxi boat drivers (er, skippers, captains?) and discussed route and money and chose the one we felt was the best for us. Spending an hour or two in a comfortable boat with an informative and engaging skipper taking you where you ask him far exceeds any group tour IMO. The price is higher, but if you have 3 peeps, the overall price starts to approach tour pricing. So, skip the tour, mingle with the taxi folks and pick the one that your group likes and have a ball. That’s what we do now.

PS: Bonus points for picking the best cabbie that has a cooler of Heineken.