Canada Post expects Thursday will be its busiest day of the year.
And FedEx is targeting Monday globally as its highest-volume day of 2012.
Canada Post estimates the holiday rush will see it deliver about one billion cards, letters and packages.
About nine million kilograms of mail will be delivered via Canada Post from outside the country.
Northwest of downtown Toronto is Canada Post's largest parcel processing plant, where workers are lining conveyor belts around the clock to handle the non-stop flood of holiday packages.
"In a daily basis at this time of year we're handling about 550,000 pieces a day, as we approach closer to Christmas we expect to be 700,000 pieces or more," said Randy Carroll, director of the plant's operations.
"In this facility itself we process at the rate of well over 40,000 pieces an hour."
While the bulk of Christmas mail will be flooding the system this week, there will be plenty more pouring in next week, he adds.
"We will see customers switch to (Xpresspost and priority courier service) and mail heavily all the way up to the 22nd of December," he says.
"Our motto and our goal is to have every parcel to our customer and under their tree for Dec. 25."
The Christmas season is just one of several exceptionally busy periods Canada Post faces, Carroll says, noting Black Friday and Cyber Monday really took off in Canada this year.
"We had record numbers for that week and we expect to see that continuing all the way through the Christmas period. Another big season for us is right after Christmas, it's the Boxing Day sales, and we see a huge amount of product come through here."
The growing impact of e-commerce and other retail sales is so strong that Canada Post is in the habit of watching out for big deals and promotions so they can prepare for the coming onslaught of packages.
"We're seeing a lot of uptake (of e-commerce), we even monitor The Shopping Channel and (the media) to see where sales are so we can adjust our plan for the next day — because we know when they have the sale, we're getting the mail."