Canada's Brookfield Asset Management (BAMa.TO) is planning a fresh $6.4 billion bid for Australian port and rail firm Asciano (AIO.AX) with Qatar's sovereign fund, two sources told Reuters, widening the global battle for the haulage heavyweight. The willingness of Brookfield to raise its offer and Qatar Investment Authority's (QIA) entry as a potential co-investor underscore the immense appetite for Australian infrastructure, especially mining-exposed companies whose share prices have been battered by the commodities downturn. Asciano, which had a market capitalization of $4.3 billion a year ago, said on Tuesday it was dumping Brookfield's…