In some countries around the world, workers in the service and hospitality sectors earn a guaranteed livable wage with additional benefits. In those countries, tipping for service may not be part of the culture. Canada is different, and tipping is customary. To leave a restaurant without tipping is considered inconsiderate.
Bartenders and servers generally earn minimum wage, which, depending on the province, is around $10 per hour. Some provinces have a lower minimum wage, closer to $8 for service workers, on the expectation that they will earn tips to compensate for the lower wage. Service staff usually have to pay a portion of their sales to other staff, such as those in the kitchen.
This might seem strange and you may disagree, but by not tipping, you are forcing the server is effectively paying out of their own pocket to serve you. So, unless the service is poor, please tip.
The standard tip is 15% of the total bill (or 20% for highly knowledgeable, attentive service), or a dollar per drink (a couple of dollars would suffice for a round of drinks).