I reread your first post several times carefully, and realized that I missed an important thing in your question: that you're asking about all interaction with markers, not just tooltips.
To disable all interaction with markers outside the mask, you need to override the marker drawer.
If you are using Drawing to Texture mode, you need to override OnlineMapsMarkerBufferDrawer.
If you are using Tileset mode, you need to override OnlineMapsMarkerFlatDrawer.

Something like:

using UnityEngine;

namespace InfinityCode.OnlineMapsSupport
{
    public class MaskedMarkerDrawer: MonoBehaviour
    {
        public OnlineMaps map;
        public RectTransform mask;

        private void Start()
        {
            if (map == null) map = OnlineMaps.instance;
            map.control.markerDrawer = new Drawer(map.control, mask);
        }

        public class Drawer : OnlineMapsMarkerBufferDrawer
        {
            private RectTransform mask;

            public Drawer(OnlineMapsControlBase control, RectTransform mask) : base(control)
            {
                this.mask = mask;
            }

            private bool IsPositionMasked(Vector2 position)
            {
                return RectTransformUtility.RectangleContainsScreenPoint(mask, position);
            }

            public override OnlineMapsMarker GetMarkerFromScreen(Vector2 screenPosition)
            {
                if (!IsPositionMasked(screenPosition)) return null;
                return base.GetMarkerFromScreen(screenPosition);
            }
        }
    }
}

The main problem is that markers still have mouse events handled through IMGUI, since they are handled by the OnlineMapMarkerBase class, this means that when I hover over a marker, the mouse cursor is detected through the markerColliderRect , which I believe are always managed through IMGUI, and not UGUI. so this is not possible to disguise it, at least I think.
I also don't think markers are gameobjects, so you can't assign component buttons.

Thanks!

By default, tooltips are drawn with IMGUI, so this will be displayed on top of uGUI.
The best way in your case is to draw tooltips using uGUI.
Example:
https://infinity-code.com/atlas/online- … ample.html

I have created an interface google maps like, I have inserted my 2d map in a canvas, then later i created a mask and i applied it on it to make the interface a little more pleasant, the problem is that the markers i generated, don't they seem to be maskable, so I can always interact with the markers even when I'm not with the pointer over the map,
Does anyone of you have an idea how to fix the problem and avoid interactions with markers when they are under the mask?