The specific word you mention is pronounced as written. Perhaps what is making it sound a little different is that the accent in the word occurs on the 4th mora, on the ル. That naturally gives the 'ru' sound a slight emphasis as the pitch of the word goes from high to low on that sound. So while it is not the case that the ブル is pronounced as 'br', there is an accent on the 'ru'.
(2) Kana are not always pronounced as spelled but in the majority of cases they are. There are exceptions, of course. Here are some common ones:
'Long Vowels': So-called 'long vowels' occur in sounds such as とう where it is pronounced as とー (e.g. おとうさん is pronounced おとーさん rather than おと'u'さん with a full う sound).
Polyphonic characters: Another obvious example is the Hiragana characters は and へ. When は is a topic marker it is pronounced 'wa' and when へ is a particle indicating motion it is pronounced as 'e'.
Devoicing: Sometimes words contain devoiced sounds such as the す in the ます verb ending or the す in すき.
I'm sure there are more examples, but my point is that while these exceptions do exist, the majority of Japanese words are pronounced as they are written.