Waves were still approaching 20 feet after being in the 23- to 26-foot range Monday, the Canadian Broadcasting Corp. reported.
Two Canadian coast guard vessels, a Hercules aircraft, a helicopter and a private plane were scanning an area of the Atlantic that had grown to more than 7,800 square nautical miles.
A U.S. Coast Guard plane was expected to join the effort.
Crew members of the 44-foot Miss Ally disappeared Sunday in rough weather in the Atlantic Ocean about 75 miles southeast of Liverpool.
A U.S. Coast Guard plane spotted what it believed to be the boat's life raft Sunday night and dropped a buoy to mark the site. Poor visibility prevented the plane from telling if anyone was aboard.
Lt. Peter Ryan of the Joint Rescue Coordination Center in Halifax said the boat's emergency beacon was detected shortly after 11 p.m. Sunday local time.
However, weather conditions were "extremely poor," he said, with blowing snow and up to hurricane-force winds.
A search helicopter spotted the overturned boat and a life raft Monday morning. Two coast guard vessels were able to reach the area.