The lease rent is based on lower end of market rent in nearby equivalent housing while member's rent is based on the financial needs of the coop according to budget and usually divided among the dwellings on a per square foot basis. The rents are generally reasonable enough although some groups face pressure due to a lack of government funding. Some groups can afford to reduce member's rent further by means of a special reserve while other groups do not have such reserves. Availability of such funding vary from group to group and are also tending, unfortunately, to disappear. Yes you can, but the fact that you are a member of one group gives no priority in another.
Units can become available for many reasons, personal, professional, etc.
Usually a group will require a minimum of 3 months' notice. By law, a member who occupies co-op housing is considered a tenant and subject to the applicable articles of the Quebec Civil Code. The Rental Board publishes a mandatory lease agreement specific to housing co-ops. The other non profit housing groups must use the regular lease. There are apartments of all sizes within the community.