it改为that
it虽然可以作为代词，但是后面不能跟限定语，即of the United States.
这里的it 指代不明确 你是指代美国的政府系统 还是美国的加拿大的政府系统？有歧义
改成the one
The federal system of government in Canada is similar to the one of the United States.
最好事不用代词
The federal system of government in Canada is similar to the federal system of government of the United States.
把it改为that
因为that可以指代the federal system而it则无此项用法
