See I think that almost makes sense to think that, as without the ë is technically is like jo/joe same with Zoe and Zoë the diaeresis tells you that you pronouce the e rather than run the vowels together in a diphthong
French/Canadian stylee is apparently correct. Some boating bores clever people pronounce it bom-bar-DEE-yeh and some pronounce it bom-bar-DEE-yay - tis much easier now they are generally known as BRP ?