ICAEW has reciprocal arrangement with CICA, means a member of ICAEW would have to pass reciprocity exam of CICA and satisfy other requirements. CICA might ask such member of ICAEW from Pakistan to satisfy experience requirement in CICA ATOs here in Canada, as CICA generally does not accept Pakistani public accounting experience to satisfy CICA's experience requirement.
USA follows its own GAAP (simply speaking accounting standards), however, ICAEW follows IFRS/ IAS which are different than US GAAP (though similar). Thus, currently there is not much demand of ICAEW to work in USA, unless someone finds a job where conversion of financial statements from one standard to another standard is required. However, after harmonization and integration of two standards, demand of said designations may increase in future.
Moreover, both Canadian and US employers know more about their own designations, so mostly prefere those. An ICAEW member may find jobs in Canada but cannot be called as CA or write with his/her name "CA" unless he/she is a member of CICA.
Conversion from global designations available these days in Pakistan toward Canadian designations is more easy as they have formal acceptance arrangements and advance standings.