Chickens generally do quite well in winter provided that the breeds you have are suitable for our Canadian climate and that they are provided a dry, draft-free, warm shelter.
Some breeds are more suitable for our Canadian climate than others. Breeds that have originated in Northern climates share common traits that help them adapt to cold weather including a larger body mass, heavy feathering, and small combs/wattles to help decrease the risk of frostbite. Some examples are Australorps, Dominiques, and Wyandottes.
It is essential that your coop is set up to provide the birds with a dry, draft-free, warm shelter. The lightweight, non-insulated chicken coops that you find in many farm supply stores are not suitable for winter conditions! People often ask, “What temperature does the coop need to be at during the winter?” There is no exact answer, as it will depend on the breed and how winter hardy your coop is. In general, the coop should not feel warm to you on a cold winter day. The birds will not become acclimatized to outdoor temperatures and could potentially become sick if there is a huge swing in temperature from the inside of the coop to the outside. Observe the birds behavior as an indicator if they are too cold. If you notice your birds are huddling in one place all day long, are lethargic, or reluctant to move, they are too cold and you need to take implement additional measures.
Whether you have 5 chickens or 50, the same principles apply for making sure the birds do well during colder temperatures:

Water is of the Utmost Importance! All chickens in the coop need access to clean water during the winter that is NOT frozen. Common options are a heated pet bowl or a heated waterer designed specifically for poultry. The heated pet bowl is usually a cheaper option, although is likely to get dirty quicker. If you do not have a heated water source for the birds, be prepared to go out to the coop several times during the day to provide water that is not frozen. It’s important to make sure that even in winter the waterer is cleaned often to prevent bacteria from growing and kept free of any debris.
Stock up on Scratch and Feed!  Scratch is a mixture of different grains.  Scratch is reserved for winter as it helps raise the bird’s internal body temperature. It is not a complete diet, and needs to be fed in conjunction with a nutritionally balanced feed. Ideally it should be fed during the evening so the birds can digest it throughout the night. Only feed the birds what they will consume in 10-15 minutes. Make sure you also have ample quantities of feed. Chickens will eat more as the temperatures drop to help stay warm. Water is required for them to digest their food properly; the importance of water that is not frozen cannot be over-stressed!
Keep the Coop Dry! Resist the urge to close up vents on the coop to preserve heat! Adequate ventilation is a must in the winter time to keep moisture and ammonia out of your chicken coop. Even at mild temperatures, chickens can get frostbite if the moisture content in the coop is too high. A good rule of thumb is, if you start to see condensation or ice forming on the windows in your coop you do not have enough ventilation! You can achieve ventilation in many ways in your coop but it is ideal if the vents are placed high on the walls, on at least two different sides, and are protected from driving rains and snow. Make sure to remove chicken manure daily to remove excess moisture. Provide your chickens with lots of dry bedding material (4-6” is ideal) and clean up any wet litter right away. Wet litter also creates favorable environment for bacteria. Look for bedding material that has good absorption and retains warmth.
Eliminate Any Drafts! Just like us, chickens are susceptible to wind chill effects. Take a good look around the inside of your coop – are there any gaps or holes (not intended for ventilation) that could let in a draft? They should be sealed. If you are adding insulation to your coop, make sure it is covered from the chickens or they will try to eat it.
To Heat or Not to Heat? A hotly debated topic is whether to add a supplemental heat source to your coop or not. If, despite all of your best efforts, the chickens are still too cold you will need to consider adding heat. Heat lamps should be avoided AT ALL COSTS! They are a severe fire risk and there have been numerous cases of chicken coops going up in flames in mere minutes. For most small coops, a flat panel zero clearance radiant heater will work well. These heaters take up minimal space, use little electricity, provide a safe source of heat, and will keep the chill off in your coop. They are available at hardware supply stores. You may want to consider adding a weather station to your coop to monitor the temperature and humidity.

Additional Tips and Tricks:
Consider securely attaching a tarp to the outside run to create a wind break. This will keep inclement weather outKeep the outdoor run covered as chickens dislike walking in the snowUse wide roosting platforms, such as a 2” X 4” with the wide side up. This allows the chickens to cover their feet on the roosts with their feathers, reducing the risk of frostbiteConsider adding environmental enrichments in the winter time when chickens are prone to becoming bored from being ‘cooped’ up. Add new perches, tree stumps, logs, a head of cabbage, etc.

Source: Latest from Alberta Farm Animal Care