Why title alone doesn't decide it
A common misunderstanding is that whoever's name is on the deed controls what happens to the house. In Ontario, the matrimonial home rule works differently — it generally protects both spouses' rights to the home regardless of legal ownership, meaning both generally need to consent to a sale, a mortgage, or other major dealings with the property while it remains the matrimonial home. This is exactly the kind of detail worth confirming with a family lawyer specific to your situation, since exceptions and court orders can change what applies.
What tends to happen practically
Couples in the process of separating or divorcing generally have a few common paths: sell the house and split proceeds according to their settlement or a court order, one spouse buys out the other's interest and keeps the house, or the house is held temporarily while other parts of the separation get sorted. Which path fits depends on the specific separation agreement or court order in place, and that's a legal and financial question best worked through with a family lawyer, not assumed from a general description.
Why a cash sale sometimes fits this situation
A sale during separation often needs to move without dragging into a long showing-and-negotiation process, and a certain, no-financing-condition close can reduce one more variable during an already complicated time. That said, both spouses' consent and lawyer involvement generally still apply regardless of how the house is sold — a cash sale doesn't change the underlying legal requirement, it just changes the process once everyone's agreed to sell.