//
        private UserControl LoadControl(string UserControlPath, params object[] constructorParameters)
        {
            // add this to aspx page that needs to load a .ascx control
            // http://www.effegidev.com/post/WebUserControls-and-Parameters.aspx
            List<Type> constParamTypes = new List<Type>();
            foreach (object constParam in constructorParameters)
            {
                constParamTypes.Add(constParam.GetType());
            }
            UserControl ctl = Page.LoadControl(UserControlPath) as UserControl;
            // Find the relevant constructor
            ConstructorInfo constructor = ctl.GetType().BaseType.GetConstructor(constParamTypes.ToArray());
            //And then call the relevant constructor
            if (constructor == null)
            {
                throw new MemberAccessException("The requested constructor was not found on : " + ctl.GetType().BaseType.ToString());
            }
            else
            {
                constructor.Invoke(ctl, constructorParameters);
            }
            // Finally return the fully initialized UC
            return ctl;
        } 
        //

//
        private UserControl LoadControl(string UserControlPath, params object[] constructorParameters)
        {
            // http://www.effegidev.com/post/WebUserControls-and-Parameters.aspx
            List<Type> constParamTypes = new List<Type>();
            foreach (object constParam in constructorParameters)
            {
                constParamTypes.Add(constParam.GetType());
            }
            UserControl ctl = Page.LoadControl(UserControlPath) as UserControl;
            // Find the relevant constructor
            ConstructorInfo constructor = ctl.GetType().BaseType.GetConstructor(constParamTypes.ToArray());
            //And then call the relevant constructor
            if (constructor == null)
            {
                throw new MemberAccessException("The requested constructor was not found on : " + ctl.GetType().BaseType.ToString());
            }
            else
            {
                constructor.Invoke(ctl, constructorParameters);
            }
            // Finally return the fully initialized UC
            return ctl;
        } 
        //

http://www.effegidev.com/post/WebUserControls-and-Parameters.aspx

Aspx Load User Control with Params

C#