Choosing a groomer is a very personal decision and depends very much on the breed of dog you have.
Unfortunately the grooming industry is not regulated in Canada so it is up to the individual groomer to uphold good grooming practices and a clean environment in which to practice their trade. There are grooming schools that provide a good grounding in the skills needed to groom, but very often the individual groomer should pursue further education to enhance their understanding of different cuts specific to unique breeds. In Ontario the ODGA (Ontario Dog Grooming Association) provides guidelines and further training opportunities for groomers; this would be a good place to find information about groomers who participate in these programs.
Finding a groomer that suits your needs depends on what it is you are looking for. If you have a specific breed, e.g. a schnauzer or poodle, you would need to chat with each groomer to determine how much experience they have with that particular breed. Very often breed specific grooming can be expensive and must be done on a regular basis, so consider this cost when choosing your breed. Most breeds can be groomed in a fairly generic manner making the coat a little easier to manage between grooms. For example a poodle can be clipped in one of the typical poodle cuts, but this must be upkept every 5-6 weeks, however a short generic trim can sometimes last 8 weeks.
Go and meet with your groomer, ask about cleaning procedures for brushes, combs etc. Is the groomer prepared to allow you to tour the whole premises, can you see some pictures of completed grooms? Some groomers will be able to accommodate a short stay for your small dog especially if they are particularly nervous which will eliminate the need for them to stay all day. However, a longer stay will be needed if your dog has a thick or long coat, as this allows the groomer to ensure the coat is thoroughly dried before leaving for home. Also to be considered is that older dogs sometimes need a break from the grooming process and so a longer time at the groomers is not always a bad thing. This means that they will have time to have a bathroom break and a little rest at some point during the day. These are things to consider when booking appointments.
At the end of the day, what we are all looking for is someone who will care for our dog with their best intentions and listen to our needs as well as the needs of our dog. Relationships with groomers can last for the lifetime of your dog and are therefore very important to develop and nurture.