A couple of good ones are: Quality Hotel & Conference Centre http://www.choicehotels.ca/en/quality-hotel-&-conference-centre-oshawa-hotel-cn971?promo=gglocalcaen
and BEST WESTERN PLUS Durham Hotel & Conference Centre
Good luck with the event.
Another good venue would be Ajax Convention Centre as it has 3 hotels in the parking lot basically from value minded to executive suites
I am a Wedding Officiant and I do a lot of weddings at Ajax Convention Centre, 550 Beck Cres in Ajax. There is a hotel that your guests could walk to just across the parking lot, on both sides of the Convention Centre. Hope this helps.
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