Threatening swerving by driver - should I report it? (Canada)
I also live in Ottawa so I can provide some pertinent viewpoints.  Yes, you should report it, and yes, it will probably be an exercise in frustration. Don't expect the police to do anything about it. However, you should report it anyway, it might end up in a database somewhere and give them another data point about why it's important to build more cycle lanes and increase driver education on the issue of cyclists.  If they notice a trend of complaints against the same vehicle, perhaps they will be able to do something about it.

A little anecdote.  I once saw a car ram into the back of another guy's car at a stop light. The driver in question fled the scene. I was able to catch the license plate as I was walking down the sidewalk at the time of the accident.  Even though the police were able to find the car, and identify that indeed it matched the description and damage, they were unable to press charges for fleeing the scene because the owner of the car claimed he wasn't driving, and the police therefore didn't have enough evidence to actually issue a ticket or charge the suspected driver.

Without video evidence, there is probably little they can do to actually issue a ticket.  

If you are uncomfortable making this turn because of the high amount of traffic and because of incidents like this. You can just head straight on Rideau across the intersection and then wait for the light to change and then go straight across Sussex.  This will avoid a lot of traffic and won't add much extra time to your commute.  You might even possibly avoid issues like this in the future.  It's not great that cyclists have to ride so defensively, but it's better to be safe than sorry.

Hopefully this situation won't turn you off cycling. I've found that most of the drivers in the city give quite a bit of room to cyclists, but there are always bad apples in the bunch.

One last point, if you want to ride the city without having to deal with traffic, check out the CN Cycle for CHEO. You got 2 weeks to get ready, and it's a great way to see the city and help a worthy cause.