* Harper to unveil new cabinet Wednesday morning
* Flaherty cancels speech, source says nothing unusual
* PM has five senior cabinet slots to fill (Updates with comments on finance minister canceling speech)
OTTAWA, May 17 Canadian Prime Minister Stephen Harper will announce his new cabinet on Wednesday to fill five senior slots in the wake of the May 2 election that his Conservatives won, officials said on Tuesday.
Finance Minister Jim Flaherty, widely expected to keep his post, canceled a planned speech in Boston he had been due to give on Thursday, the event organizers said on Tuesday.
A senior government source said the speech "was never really written in stone" and that the organizers had in fact been told last week that Flaherty would not be attending.
Apart from Flaherty, the biggest question is whether Industry Minister Tony Clement will stay in that position.
Clement is currently reviewing a proposal by the London Stock Exchange (LSE.L) to buy TMX Group (X.TO), the operator of the Toronto Stock Exchange.
Harper will unveil the new cabinet at 11:15 Eastern (1515 GMT). He has five senior cabinet positions to fill after the election, when the Conservatives won a majority of seats but some ministers were not re-elected.
The vacant posts are at foreign affairs, transport, veterans affairs, the treasury board and intergovernmental affairs. (Reporting by David Ljunggren; editing by Janet Guttsman)