George Smitherman says AECL has already made its bid and adds the group that worked on that proposal remains intact.
Smitherman says he sees no impact on the ongoing process and that Ottawa's announcement shows the federal government supports AECL.
Federally owned AECL is one of three companies bidding to build new reactors at the Darlington nuclear station east of Toronto as part of a provincial plan to expand and refurbish its fleet.
The federal government now says the Crown company is being put on the block in the hopes of boosting global sales of Candu reactors Â– part of a major restructuring that will also mean private-sector management for AECL's Chalk River research facility.
AECL is up against Areva Group of France and U.S.-based Westinghouse Electric Co. for a contract to build two nuclear reactors in Ontario.
Smitherman says Ontario is still working toward a June 20 deadline but is unlikely to have made a decision by then.
Premier Dalton McGuinty has hinted in the past that the government may opt for AECL because as the sole domestic bidder, a contract with that company would create jobs in hard economic times.
Critics say choosing AECL could mean higher costs, noting the price tag for building reactors has more than doubled in the last three years, and taxpayers risk being stuck with the bill.