E3 visa expiring in nov 2015 but i94 valid until mar 2017

Hi sir/madam,

My husband is on e3 visa (work authority for Australian citizens) and it’s going to expire on nov 2015.Due to family emergency we travelled to India in April and we came in july.while entering into USA the Border Security Officer issued a i94 until mar 2017. Now my employer trying to file a extension of visa but he is not able to do due to i94 valid date .We went to local USCIS there they were saying that we can stay here and work here legally until the i94 date.If we want to travel outside of the country we need to apply for new visa.My question is whether we can apply extension of visa from USA or do we need to apply from other country.can we apply visa renewal of visa from Canada.If so please let us know the process. Thanks in advance