Hi,
1st of all, the Master's Graduate stream you are talking about, is not Ottawa PNP but is one of the PNP programs started by the Ontario province. True, on paper Ontario Master's graduates passing out form eligible ON based public universities are eligible to apply for direct PNP nomination, without need of a job offer.
But, if you see the conditions attached to it, you will realize that getting PNP nomination under this Master's graduate stream is not straightforward. The main factor is the volatility and the set quota of this PNP program. Last year they this program was in pilot mode with quota for only first 1000 applicants. This year it has been upgraded to a non-pilot status with a set target of 1300. Next year we don't know..what it will be. And given there are thousands of Master degree holders coming out of Ontario based universities... chances of you or any other Master's student fitting into that 1,300 set quota is not assured. So, you may..or you may not be among those 1,300 students rushing to submit their application to get PNP nomination from Ontario province under this Master's graduate stream. Not to mention, you must meet other conditions like maintaining personal bank account monthly statements for the past 6 months (while studying), or (if overseas) an original letter and monthly statements from a recognized financial institution indicating personal account standing/balance of minimum 11,086$ for 1 person. This means apart from the tuition fees+ living expenses, you must maintain/show personal bank balance of minimum 11,086$ for the immediate past 6 months before applying for PNP nomination..and that can be an expensive affair.
http://www.ontarioimmigration.ca/en/pnp/OI_PNPSTUDENTS_MASTERS.html
http://www.ontarioimmigration.ca/en/pnp/OI_PNPSTUDENTS_MASTERSAPPLY.html#_qualify
Also, do keep in mind... that reality is, any of the student immigration programs across Canada (except for Quebec programs which changes after every 4 years, and after revision of rules this year, next revamp will be on 2017) can change anytime. So, it will be very unwise to completely rely only on Ontario Master's Graduate stream for securing PR. What if this stream by chance shuts down next year?
If PR is what you are seeking, then rather you should look into provinces of Manitoba,Quebec (if you can learn higher intermediate French) or B.C (if you pursue specific master degree sin Engineering,CS/IT, Agriculture, Mathematics, Biological and Physical Sciences etc.). these provinces have comparatively direct PR routes for Master degree students and best part no quota like in Ontario.
Also... 1 year study and then 1 year PGWP is not an issue to apply for PR under CEC, after completing your MBA degree. You see, you will have max 2.5- 3 month's buffer time till you get PGWP. Add that time and constant networking right from the 1st day of your class, possible internships and good luck, you may get a skilled job by the time you receive your PGWP. And even if your PGWP falls short before you can get PR (i.e after completing 1 year and already applied for PR under CEC), you will be eligible for bridging visa till the decision on your PR comes. So, it's very possible to secure PR under CEC with a 1 year PGWP, provided you do this MBA from a good university, work hard, excel and do reasonable networking.
Best of Luck.
***All opinions expressed are purely personal, and pieces of information mentioned are to the best of my knowledge... You should consult other sources too.