They can identify cultural with one such as they view themselves more English than French. It is not a denial of their heritage to have a stronger cultural identification with one over the other. Similarly, for children of interracial couples. I realize that there is an issue of color and the racism that goes with color. For instance, we are very willing to accept a very light skin person as black but would have a difficult time accepting a very dark skin person as white.
Race is a social construct.
We have enough problems with the social constructions that we currently have. Introducing a new construction complicates not relief the issue. As for Hispanic, Hispanics are a ethnic construct that is separate and different from the racial construct. Hispanics don't get to choose to Black or White, any more than Jews don't get to choose Black or White. There are Black Hispanics just as there are Black Jews.