As far as accent goes, there is a continuum, and it depends on where people are from. There are many English accents, and it doesn't really matter which you learn, as you will be understood by all English speakers.
Canadian English sounds more like American English (with the exception of the provinces of Nova Scotia and Newfoundland, which sound more Irish, and Québec, which can sound more French if people aren't native English speakers). As a Canadian, I have a hard time with some southern American accents; Louisiana and Alabama are two examples. Canada as the USA form a dialect continuum, meaning, as GregS said, that a Canadian and American living close to the border will sound more like each other than their compatriot from the other side of the country. For example, people from Vancouver (Canada) and from Washington (USA), which are very close to each other, sound almost exactly the same, where as they both sound nothing like people from St John's (Canada) or Baton Rouge (USA).
As a linguist, I can hear some differences between Canadian and American accents usually, but to the untrained ears, those differences are minimal. In fact, the differences are so minimal that Canadian English is often classified as a type of American English.