My grandfather immigrated to the US shortly before 1900. What was required to leave Canada at this time? How can I find out exactly when he did come to the US? I have found him in a city directory for the year 1900 but have not been able to find out if he ever became a citizen.

See Immigration Records for information on what was required to leave Canada. US census records should indicate whether or not he became a US citizen (at least prior to 1930), or you search Naturalization Records

From Jo Ann - You didn't need anything to leave except for the means to do so. I have a number of ancestors who left Ontario and Quebec (mostly for economic reasons) 1870 through about 1910 and came earliest via horse and wagon. Later, they came by train. My mother said that her grandparents came in a group and people would put their possessions in open boxcars. These were the French-Canadians. Nearly all of my ancestors were farmers or farming connected. Later it depended upon where you left from. Easiest from Sask. Ont. and harder without ID papers from Que. through NY, Vt or Maine. Need to check US Archives and need to know where they came into States.