I'm in the greater Toronto area and the end of April can be lovely and spring like, freezing cold, or way too hot. Doesn't help much, does it.
I'd suggest a few days before leaving that you check:
http://www.theweathernetwork.com/ind...ecode=caon0696
It's the 14-day weather trend for Toronto. I usually don't believe it much more than 7-days out, but it will give you an idea of what's expected. You can see that the historical high is 12C for the next 14-days, with some predicted above and some below.
I'd think you're likely going to get decent spring-like weather around 15C, but who really knows.
Evenings will be cool though, possibly close to zero Celcius. That's the overnight temp though, evenings won't be quite that bad. If you're going to be outside during the evenings you will definitely need heavier wear.
www.weather.com is the US weather site, although you can likely get Toronto's info there as well.