Hwat for what is the original pronunciation and was the only form used in Middle English. In Modern English, many dialects lost the wine-whine distinction, and began pronouncing words spelled "wh" as simply "w", rather thn "hw". The original, conservative form is still around, and is considered standard in certain areas. In North America, many Southern accents preserve it. Elsewhere in N. America, it has almost completely died out, except in older speakers. However... people often hear others using it, and hear that it sounds old-fashioned and a little bit more correct, and thus add it to their own speech. I remember myself adding it to my speech for awhile. However, I've given up the habit. My grandpa has it, but I can tell that he must have consciously added it to his speech, and it is not a relic form, because he occasionally hypercorrects--he sometimes pronounces words like "wine" as "hwine". So, it is sort of similar, in the way that people add relic forms to their own idiolect--sort of like "ahnt" for "aunt", which only natively exists in New England, and certain cultural dialects but people all over North America have added it to their own speech, because it sounds very cultured--that is how many pronounce it in Britain, and because it allows you to contrast it with the word "ant". Also, unlike the cot-caught merger, or the pin-pen merger, people can hear the difference between "wh" and "w", even if they have merged them. People with vowel mergers, such as the cot-caught or pin-pen mergers, cannot normally hear the difference between the two vowels at all and thus do not notice people that do distinguish them. They simply assume that it is another case of English spelling that spells two words differently but they are pronounced the same way, like meet and meat. Thus since they can't hear the distinction, they do not consciously add it to their speech, unless someone else points it out to them, and demonstrates the difference to them. I can't hear a difference between cot and caught for example (well, now I can, sort of, because I have learned to distinguish them if necessary), but I can hear the difference between "wine" and "hwine", or "wat" and "hwat".
Some Scottish, and Irish dialects, as well as some others have a Spanish "r" sound, rather than the retroflex "r" used in General American English. Conservative Received pronunciation used to pronounce r's between words as a flap.