I have a similar situation in Vancouver; riding along Kingsway from Boundary to 12th Avenue is a km or so shorter than the off-road bike routes that get me to the same place, and the bike routes have more up & down while Kingsway is mostly downhill for the duration (several kilometres); it usually cuts about 5-7 mins off my ~57 minute ride if I take Kingsway.

The downside: traffic. It's 3 lanes with no parking during the morning rush, and while there is plenty of room in the left two lanes, drivers get aggressive and honk/cut close when jumping in front of me. It's regular sidewalks on both sides of the road, but I'd prefer not to ride on the sidewalks: with the pedestrians and the ramps etc, my speed necessarily drops and I end up losing the speed advantage of the route.

Anyways, I end up just taking the off-road routes now. Takes a few mins longer, but is more enjoyable, and there's about 50m more climbing due to the up & down, resulting in better training and more calories burned.

If you have the option, I'd look into alternate routes that are more bike-friendly.

Out of curiosity - is the wide sidewalk designed for bikes? What I mean is, are there signs or painted bike logos on the pavement or something that indicate that bikes are welcome there? If so, I'd probably keep riding there and not worry too much about startling pedestrians; they should probably be paying more attention if they're walking on a bike route. If it's not marked and pedestrians aren't reasonably expected to be looking out for bikes, I'd probably avoid that route if possible.