回複：取得加拿大綠卡如何回美國

It is better for you to land Canada at the time your 6-yr H1b expires. If you want to land Canada and come back before your H1b expires, the border agent may not let you in because you can't extend and change your status at that time.

When your H1b status expires, you have 10 days of grace period to leave US. When you leave US, by land or by air, you need to surrender your I-94 to inform USCIS when you leave. Otherwise UCCIS' record still shows that you are in US even though you have left.

You can apply for 10-yr B visa after landing. However, you need to demonstrate that you have no immigration intent to US and strong ties in Canada. It is not guaranteed that you can get the 10-yr B visa.

You need documents to show that you have lived in Canada for at least 1095 days within four years to qualify for citizen application.