Not sure if this is an option you've considered but I also have offices in Downtown Toronto however, mine are @ Bay and Queen. I leave the bike @ the Go Station and take the train in to Union. I wear my jacket and boots to the office and have a pair of shoes I can change into. At the end of the day, my jacket and boots come back on and I am on my way to Union to catch my train home. Of course my advantage is that I use the Lakeshore West line so have a lot more frequent trains available. At the end of the year, I print out my Presto statement and use it in my taxes.
I know this probably defeats the purpose of what you are trying to achieve and there are a lot of people who ride into Toronto however, with the never ending construction and congestion, the upcoming Pan Am games which will lead to further congestion and the distracted mindset of Toronto drivers who are busy talking/texting on their phones or road raging, etc. I find it a more preferable solution than riding in. Of course I do ride in when I need to visit the dealership or on the rare occasion when we are working on a weekend.
You have already received some excellent advice on routes to take, nonetheless I thought I'd throw this in as an alternative.
Cheers!