Hurricane Sandy is expected to change into "a large and intense post-tropical cyclone" on Monday as it heads toward the northwest and into Canada, Environment Canada warned Sunday.

"It is possible that this transition could intensify the storm slightly further prior to moving inland somewhere along the New Jersey coast late Monday night or Tuesday morning," the agency said on its site.

Heavy rain and wind is expected to hit southwestern Ontario the hardest between 10 p.m. Monday and 5 a.m. Tuesday.

"The remnants of hurricane Sandy will arrive late Monday as a large and powerful post tropical fall storm over Southern Ontario," Environment Canada said in a statement Sunday." The Northeastern United States will take the brunt of the storm, however, there is also the potential for significant impacts in Southern and Eastern Ontario."

A stalled front over Southern Ontario will combine with "moisture-laden post-tropical storms" to produce potentially significant rainfall.

"Persistent rain is forecast near this front for Sunday and Monday

leading up to the arrival of Sandy," Environemnt Canada said. "It may amount to 10 to 30 mm over this period, especially across Niagara, southcentral Ontario and north to Georgian Bay."
And when Sandy moves in, an additional 30 to 50 mm is possible, centred on the St. Thomas, ON area.

The Toronto area can expect winds of 60 km/h with gusts of between 80 and 100 km/h, but will be slightly more powerful in the Hamilton, ON area, according to Environment Canada.

"These gusts could cause broken tree limbs or in some cases uprooted trees which may result in downed utility lines. Residual falling
leaves can also obstruct storm water drainage systems along roadways particularly in urban areas.
This combined with heavy rainfall could increase the risk of flooding in some areas," Environment Canada said.

Gale to storm force winds are anticipated on the Great Lakes and St. Lawrence River with the strongest winds -- "possibly severe" -- in the St. Lawrence Valley between Montréal and Quebec.

Quebec is expected to see 20 to 40 mm of rainfall, which will also affect the Maritimes.

The rain could mix with or change to snow over parts of south-central Ontario and western Quebec as temperatures approach the freezing mark north and west of the storm, forecasters said.

On Saturday, meteorologist Mark Robinson at the The Weather Network said, "As many as 23 million Canadians stand to be affected by this storm. That's 70% of the (country's population)."

And Canadian Hurricane Centre spokesman Bob Robichaud told the network that "everyone in the Maritimes, certainly everyone in southern Quebec and eastern and southern Ontario, should be monitoring this storm."

"I know it's a big area but it speaks to the size of this storm. ... It's getting a lot of attention and deservedly so."

On Sunday, the Emerald Princess, a 15-storey cruise ship carrying nearly 5,000 passengers to the Maritimes, docked at the Port of Saguenay, QC because of the impending storm. "Due to the presence of Hurricane Sandy and the impact it will have on the New England area, the port calls to Bar Harbor, Boston and Newport, RI have been cancelled," Princess Cruises, the owner of the ship, said in a statement.

Tropical cyclone Sandy revved back up to hurricane strength on Saturday as it churned toward the U.S. northeast coast, where it threatens to become one of the worst storms in decades.

The late-season storm has been dubbed "Frankenstorm" by some weather watchers because it will combine elements of a tropical cyclone and a winter storm.

-- with files from Terry Davidson, Danny Gauthier and Reuters