Why would the USA want all of Canada, Mexico, and North America? That being said, I can see a time line where the USA has more of North America.
1.) The USA is more successful in the ARW. This could be possible by capturing and holding what would be become Upper Canada in 1779. I like the time line also where Nova Scotia joins the other 13 colonies in 1776. So from the ARW, the USA has Ontario and Nova Scotia.
This will make it easier in the future for the rest of Canada to become American by peaceful means. Also, it makes adding southern territory easier as well due to a desire to even out slave and free states.
2.) American culture is more accepting of foreigners. Perhaps even citizenship is spelled out better in the US Constitution. This will make acquiring Latin territory easier.
3.) USA buys LA purchase same as OTL
4.) The USA has better relations with Britain after the ARW. No embargo act and no War of 1812.
5.) Instead of splitting the Red River territory in 1818, the USA purchases it and keeps the Milk river territory. This gives the USA the best part of Manitoba and Saskatchewan plus a little of Alberta.
6.) USA annexes Texas in 1836 after it wins independence to equal out slave and free. This makes Mexico mad, War with Mexico nets USA New Mexico and California including baja California.
7.) USA supports Rio Grande republic in 1840, it is victorious and wants to become part of USA. USA annexes and takes Chihuahua and Veracruz states in Second Mexican War.
8.) Polk has campaign goals of settling Oregon question, Acquiring more of Mexico
The Oregon question is settled, the USA buys all except for Vancouver Island from the British. Polk also purchases British Honduras.
9.) Polk makes the Gadsden purchase for all of Sonora, Durango, Sinaloa and Zacatecas. USA gives British Honduras to Mexico. Also states that Mexico can absorb Guatamala and Honduras if wanted. This is the last of US possessions in Mexico.
10.) Civil War occurs four years earlier after 1856 election
11.) Dominion of Canada is created. It is Quebec. Later other portions of what is left such as Northern Ontario, Northern Manitoba, and the Northwest territories are added. PEI and Newfoundland are added as well. It is pretty much a French country with some Englishmen added into the mix.
11.) USA acquires Alaska in 1867 from Russia. It is not called Seward's folly, USA is protecting Pacific Northwest.
12.) USA purchases Yukon territory, rest of Alberta and rest of Saskatchewan.
13.) In Spanish American War, USA annexes Cuba and Puerto Rico and makes the Philippines a protectorate. Along with Virgin Islands, they become the State of American West Indies.
14.) US and British good relation results in a joint effort to build two canals, one in Nicaragua (USA) and one in Panama (UK). One is for Pacific to Atlantic traffic and the other is for Atlantic to Pacific.
15.) After WWII, the USA creates an oceanic state, Pacifica out of Hawaii and other Pacific island possessions, mainly Guam and Samoa. Will also include islands captured from Japan such as Carolines, Marshal Islands, and Marianas.
So in this way, not all of Canada and Mexico are annexed but some of the best parts are.
From Canada, the USA will get the southern Ontario region which will become an industrial juggernaut. The USA will obtain the wheat fields of Manitoba, Saskatchewan and Alberta. The USA will obtain the oil fields of Alberta ...
From Mexico, the USA will obtain the oil along the gulf and in the gulf. The mines of northern Mexico will also be in the USA.