Does a U.S. permanent resident need a visa to travel to Canada?

While you may not need a visa to visit or transit Canada, you still need carry proper travel documents and identification for yourself and any children travelling with you.

When does employer must file amended H-1B petition?

When there is a material change in the terms and conditions of employment, the petitioner must file an amended or new H−1B petition with the corresponding Labor Condition Application (LCA).

Can a student change status during "grace" period of 30 days (J1 visa) or 60 days (F1 visa)?

Following completion of studies or completion of practical training, students have either 30 days (J1 summer work and travel and other categories) or 60 days (F1 visa holders) to leave the country. This time is not for changing status. Students are permitted to travel in the country during these days. 

Does B-1/B-2 need to attend interview when he files for the extension of B-1/B-2?

A person is not required to appear for an interview. You also are not required to mail your passport.

How long can a green card holder remain outside the USA?

An absence between 6 months and 1 year raises a rebuttable presumption that continuity of residence has been interrupted. An absence of 1 year or more “shall” disrupt the continuity of residence. However, there are exceptions: