At first contact, you should be concise and provide them with all the details of your purpose of emailing them. You also may provide them with your background specifications if you feel that it's something worth sharing.
You should refrain from complimenting them and their publication record, however, you should make scientific comments on their recent publications (within 3-5 years). You don't have to read all their publications, but you should read the ones that were published in respectable journals, the ones that were published solely out of their lab without collaborators, and the ones that relates directly with what the professor needs help with (if the position was advertised). And keep an open mind when you're writing about these scientific stuff, you're not the expert nor do they expect you to be.
At the end of the day, if you are enthusiastic and polite, you should be able to obtain responses from most of them and whether or not they are available space or funding for a PhD student. Don't be discouraged if you don't obtain a response, because some emails really do get lost and never read. You should also refrain from emailing a bunch of professors within the same department at the same time, they do talk to each other and if they sniff that it's a mass-email (although it's really not), they will never respond to you.
One at a time, with personalized emails really do help, and within the Canadian institutions as a domestic applicant, this is the main way of getting into graduate school as a PhD student. I cannot say the same for international applications because there are other factors to consider, but as a domestic applicant of your own country it should be the easiest and the best way to apply into graduate school.
Hope that helps. If not, whatever.