Compare data in two dbsets

I am using a nested loop to compare data in two dbsets.  However, araccounts contains 400000 records and ffaccounts contains 6000 records.
How can I make this faster?   Thank you!
ARSalesforceEntities arsf = new ARSalesforceEntities(); //dbcontext Salesforce_FFEntities ffsf = new Salesforce_FFEntities(); //dbcontext var araccounts = arsf.Accounts; var ffaccounts = ffsf.Accounts;foreach (var ffaccount in ffaccounts) {     Console.WriteLine(++count);     foreach (var araccount in araccounts) //this line takes a very long time, about 1 min     {