public override void OnActionExecuting(ActionExecutingContext filterContext)
{
base.OnActionExecuting(filterContext);
object query = filterContext.ActionParameters["query"];
Type queryType = query.GetType();
Type modelType = queryType.GetInterfaces()[0].GetGenericArguments()[0];
var handlerType = typeof(IQueryHandler <,>).MakeGenericType(queryType, modelType);
// Here you should resolve your IQueryHandler<,> using IoC
// 'Service Locator' pattern is used as quick-and-dirty solution to show that code works.
var handler = ComponentLocator.GetComponent(handlerType) as IQueryHandler;
var model = handler.Handle(query);
filterContext.Controller.ViewData.Model = model;
}