回复：谢谢各位的回复。如果第一次只想搞定枫叶卡的话

1. 如果第一次只想搞定枫叶卡的话，必须在H1B批准后吗 （6月底开始OPT。10月1号开始H1B）？

Not necessarily. Any time.

2. 是不是在得知H1B批准后任何时候登录都可以？还是必须要拿着证明H1B批准的相关材料（比如H-1 APPROVAL NOTICE）去登陆吗？

It doesn't matter. In fact, you'd better not let Canadian immigrant officers know your H1B is approved. In other words, you need to let them believe you will NOT go back to the US and landing/settling down is the sole purpose for your trip.