Buy the largest cage you can afford. Length matters more than height. Purchase a cage for your BIRD and for ease of cleaning, not simply for looks.
Keep the perches as clean as possible - canaries use their perches as napkins and stand on them all day. Dirty perches lead to illness and foot problems. (Do not use sandpaper covers - they don't actually keep nails trimmed and they scrape the skin off of a bird's feet and cause sores.) In general, if you are comfortable, your bird should be. Avoid drastic temperature changes. Do not place your bird in direct sunlight without access to shade. Keep up your bird's food and water as canaries are unable to live long without either. Be sure that your bird's water is as clean as possible and that the hulls are blown off the seed dish regularly as canaries do not dig through their seed dish the way parrots do.