Copies of the 15-minute campaign speech, scheduled to air at 8 pm (1330 GMT), were leaked Tuesday to YouTube and Facebook.
"We know that the current constitution is not in line with democratic principles," Suu Kyi said of the 2008 charter that was pushed though by the former junta.
"Giving an obvious well-known example, the citizens know that the parliament comprises 25 per cent of parliamentary representatives who are not elected," she said.
The military appoints 25 per cent of lawmakers, who have special veto power over any legislation that might undermine the institution's influence over politics or the economy.
A criticism of the lack of "rule of law" under the previous regime had been censored out of the speech, sources from Suu Kyi's National League for Democracy (NLD) said.
All 17 parties contesting the April 1 by-election have been allowed 15-minute slots on state television to get their campaign messages across to the public.
Suu Kyi and 46 members of the NLD are contesting the polls to fill 48 seats left vacant when the current cabinet members took office a year ago.//DPA