public SearchTable(int var1, int var2, int var3)

var results = entities.vw_ToSearch.Where(x => x.var1 == var1 && x.var2 == var2 && x.var3 == var3);

IQueryable<vw_ToSearchItem> results = entities.vw_ToSearch;
if (x.var1.HasValue)
   results = results.Where(x => x.var1 == var1);
if (x.var2.HasValue)
   results = results.Where(x => x.var2 == var2);
if (x.var3.HasValue)
   results = results.Where(x => x.var3 == var3);

Where( x => x.var1==var1 &&
    (var2 == null || x.var2 == var2))