>AFAIK, if the query is executed against an instance of System.Data.Linq.DataContext linq will use Linq to Sql ; if against System.Data.Objects.ObjectContext then it will use Linq to Entities....

In our case it's an interface based on another interface class which is defined as

 public interface IContext : IDisposable
    {
        IDbSet<T> Set<T>() where T : class;
        int SaveChanges();
        void SetModified(object entity);
        void SetAdd(object entity);
        void SetDeleted(object entity);
        void ExecuteSqlCommand(string sql);
        EntityState GetEntityState(object entity);
        bool IsLoaded(object entity, string navigationPropertyName);
        void Load(object entity, string navigationPropertyName);
        DbPropertyValues GetOriginalValues(object entity);
        DbPropertyValues GetCurrentValues(object entity);
        void EnsurePaddedPrimaryKey<T>(T entity) where T : class;
        ObjectContext CoreContext { get; }
    }

And the code in the method is

var query = this._siriusContext.Max4Sale.Where(m4s => m4s.Type == max4sale.Type);

_siriusContext is an instance of this

 public interface ISiriusSqlContext : IContext
    {
        IDbSet<AccActv> AccActv { get; set; } // acc_actv
        IDbSet<Access> Access { get; set; } // access
       etc. for all other tables/views
  }