As I knew

請問加拿大公民申請必須在加拿大住滿三年後才能申請嗎?
Yes

是不是遞交申請後就可以馬上離開直到宣誓再回來?
Not exactly., because you need take a paper test in the term

期間還有什麽需要辦理的嗎?
Receive a book about Canadian history, government, etc., then wait for paper test notice, attend the test and pass the test, get new citizen ceremony notice.