You've been living in Canada for 4 years? Visiting USA "sometimes"? You're lucky your green card hasn't been canceled.
To qualify for citizenship, you need to have spent a minimum total of 2.5 years of the last 5 years physically in the US, without the length and frequency of your absences outside the US being long enough to break "continuous residence". Which generally means no single absences of 6 months or more, and no string of consecutive absences (i.e. multiple trips with very short stays in the US between each trip) adding up to about 18 months or more. Your primary residence must be the US for the past 5 years. So unless there's something else you're not telling us, like you're working for the US government in Canada, you won't qualify for citizenship for a number of years.
Were you under 18 when you got your green card? Did any of your parents become a US citizen when you were under 18?