Found this on a quick search...
"Hunting and sporting guns are allowed in provided they are going to be used for sport, or for competition. You may need to provide proof of this, such as a permit from a Canadian firearms registrar. Hunters are permitted 200 rounds of ammunition before fees are imposed, and competitors are allowed 1500 rounds. All weapons MUST be declared at the border. Failure to do so will result in confiscation of the weapon and criminal charges being brought up. A Firearms Declaration can be bought for $50 and will be good for one year.
~snip~
If you are taking hunting guns to Canada, be CERTAIN that you fill out the US Customs form 4457 with description of gun (cameras, Etc.)& serial numbers and present to US guys before leaving US (so they will have record that you took them out & didn't purchase in Canada). Also have a Canadian Firearms Declaration all filled out when entering Canada to save time & this will serve as your gun license while hunting & to buy ammo if needed." link
Firearms are divided into 3 categories-prohibited, restricted and long guns. The only category of gun a U.S. visitor may bring into Canada is a long gun, which is a regular hunting rifle or shotgun with a barrel at least 181/2 inches/47 cm, and an overall length of 26 inches/66 cm, and which does not fall into the category of a prohibited or restricted firearm. Non-restricted firearms may be imported only for sporting or hunting use while in Canada, for use in competitions, for in-transit movement through Canada or for a person's protection against wildlife in remote regions of Canada (excluding national parks) as long as the customs officer is satisfied that the circumstances warrant the importation of the firearm. Restricted weapons may only be imported for the purpose of attending an approved shooting competition in Canada. A temporary permit to carry is required. Nonresidents arriving at a Canada customs port must declare all their firearms, including long guns. Anyone who illegally carries a firearm into Canada is subject to a number of penalties, including seizure of the weapon and the vehicle in which it is carried. It is against the law for visitors to bring handguns into Canada. Personal protection devices such as stun-guns, mace or pepper spray are also prohibited.