For the binding to the property in your viewmodel to work, its mode needs to be set to OneWayToSource. I've prepared a small sample project to demonstrate this.
Otherwise, you would need to initialize a new SuggestProvider in your viewmodel which would also require passing in a QueryableCollectionView as a parameter and optionally, a SearchStateManager.
Is there a reason why the approach I suggested in my first reply would not work for you? If you would specify your exact requirement, I'd be more than happy to offer a viable solution for your particular case.
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