Diploma

The main difference between IOSH and NEBOSH is that IOSH is also a membership organization, the largest health and safety professional membership organization, as it goes. The main difference for you though will be in the qualifications, and you should find the qualification that suits your needs most, which won't really come down to the awarding body. NEBOSH doesn't offer membership, so if you are looking to join a membership organization where you can network, keep up to date with health and safety, and gain advice and expertise then IOSH is probably your best option. It brings with it plenty of benefits but how much you can benefit really depends on your situation and career goals, take a look at this article for some more information, and if you are interested, get in touch with the team at IOSH.
After IOSH, you can have a diploma in industrial safety if your age limit permits for applying for a Diploma.

Some of the PG Diploma Courses, which you can go for in Canada are:
1. Conflict Analysis and Management
2. Disaster and Emergency Management
3. Educational Leadership and Management
4. Environmental Education and Communication
Though I will recommend you to go for a Master's Degree in a subject or course related to your graduation course. Some examples can be:
1. M.Sc. In Chemical Engineering
2. Master of Applied Science in Chemical Engineering and Applied Chemistry
3. M.Sc. In Chemical and Biological Engineering
4. M. Eng. In Chemical Engineering
So, first you should decide you want to continue in same course of study or not and then choose a course for your PG.