The Liberal government says the jets will close the "capability gap" in Canada's air power as it seeks a permanent replacement to its CF-18 fleet.
It will also launch a five-year procurement process in 2017 to find a replacement, which could include F-35s.
Ottawa will continue to participate in the F-35 Joint Strike Fighter (JSF) program.
Federal Defence Minister Harjit Sajjan said on Tuesday that Ottawa will immediately begin discussions with the US government and Boeing, which manufactures the Super Hornet fighter aircraft, on the purchase of the stop-gap fleet.
Public Services and Procurement Minister Judy Foote was unable to provide an estimated cost for the 18 new jets, saying it would depend on the negotiations.
Canada cannot currently meet its commitments to the North Atlantic Treaty Organization and the North American Aerospace Defense Command with its aging fleet of CF-18s.
But the procurement process to replace the 30-year-old fleet has been rife with problems and politics.
The former Conservative government originally intended to buy 65 Lockheed Martin F-35s, with deliveries slated to begin in 2016.
In 2012, the country's auditor general criticised the sole-sourced procurement process for the fighters. Cost overruns and other issues also hampered the planned purchase.
In the last federal election campaign, the Liberals unequivocally ruled out buying the stealth bomber for the Royal Canadian Air Force (RCAF) and promised to purchase a "lower priced" option.
Canada has been involved in the JSF program, the development and acquisition program for the F-35s, since its inception in 1997.
Other countries involved in the JSF project include the US, the UK, Turkey, Italy, Australia and the Netherlands.
Canada will explore buying 18 new Boeing Super Hornet fighter jets.