Spouse open work permit ---- Please advice

[gpsv]

Hi,

I'm working in canada with closed work permit. My husband and kid got visitor visa with multiple entries.  But they are in India. My husband is planning to apply for open work permit before they travel to Canada.

My closed work permit is valid till aug-2012. My project work may possibly get extended for some more months.

1.   My concern is if he applies for open work permit what will happen to the visitor visa which he is having already?
2.   How long will it take to get the open work permit?
3.   Is there any possibility that Canada high commission rejecting the open work permit request?
4.   What are all the supporting documents which I need to give?

Please advice.