travel document needed for visa waiver countries?

Hi,

I am a Singapore citizen and a PR since 5/2004. I am back in Singapore now due to some family affairs, and will probably not be returning to Canada until 7/2010. My PR card expires in 6/2009. I have already met my 2/5 years residency obligations as of now. Therefore, I intend to renew my PR card once back in canada. But the rule says that I have to apply for a travel document in order to return. Since Singapore is a visa exempted country, I can enter Canada without a visa actually. So do I still need to apply for that travel document? I have read your forum and you stated somewhere that if I can show a return-air ticket to the transport carrier and the Immig Offr at POE, I probably dont need a travel doc. Can you pls confirm again?

My last question is: is there a maximum expired period for the PR card after which renewals are disallowed?

Thanks for yr advice in advance.