Here in Canada the green building industry is on the rise, and ECO Canada is a perfect place to go to seek out any kind of green building or environmental focused roles in construction. 
Skilled Trades Plus is a job search website tailored to those in construction and skilled trades, with many opportunities frequently being updated. 

Every summer, the Canadian Government hosts a Canadian Summer Jobs Campaign for “youth” (youth refers to anyone between the ages of 15-30). This can be a great opportunity to take a look at available jobs for the summer season. 
Career Fairs are another method of finding work. Eventbrite is a great resource as you can search “Career fairs” in your city of settlement. It will then produce a list of virtual career fairs you can attend before arriving in Canada, and in person fairs for once you arrive.  

Additionally, Construction Ontario is not only a resource and training hub, but they also have a job search page. There are also the standard metasearch websites that you can use to search for jobs in construction, such as Monster, Indeed, LinkedIn, and so on.
Taking a look at the official city website of the city you are settling in will be very helpful as they all have a job board. Use a list of Ontario Municipalities from the Association of Municipalities of Ontario (AMO) to help find your city’s website.

And finally, do not forget to pick up the phone and call small to medium sized construction companies. They do not always have time to advertise their job postings, therefore calling them to introduce yourself, explain your skillset and offer a value proposition on how you can help them can be a great strategy to find a construction job!