"What if there is no will and someone dies leaving two siblings the estate? One sibling was banished from the property - what are his rights regarding selling his portion?"
When a person dies without a will, the law in the province where he or she lived states where the deceased's estate is going to go. In order for an estate to be given to siblings, the deceased must have had no spouse, no children, no grandchildren, and no parents alive when he or she passed away. In some provinces a common-law spouse counts as a spouse for inheritance purposes and in other provinces, the opposite is true. I assume that this much has been dealt with since you say that the two siblings are going to inherit.
Assuming that to be the case, the two siblings have an equal right to inherit. They also have an equal right to be the person who applies to the court to be appointed as the administrator of the estate.
As for banishment, that is not a legal thing. You haven't said who banished the sibling or why, but despite the family disharmony that led to the situation, it doesn't matter for inheritance purposes. It will have absolutely no impact on the rights of the sibling to inherit. It was a fight and it was important to the people involved, but it has no legal force. It doesn't matter if there has been no communication between the parties since the banishment.
If the person who died wanted to ensure that his or her sibling would receive no part of the estate, he or she should have made a will. If there had been a will, the deceased could have left the estate to one sibling, or to a charity, or to his best friend, or whatever he wanted. However, in the absence of a will, both siblings continue to have equal rights to inherit.