What we call cornflour in British English, and cornstarch in US English, is flour heavily processed to remove everything except starch, giving a flavourless thickener.
If you use wheat flour you will change the flavour and also add a slight graininess as the flour grains don't completely homogenise.
If you use wheat flour you will change the flavour and also add a slight graininess as the flour grains don't completely homogenise.