When we're looking for an immigration record, it helps to make a fresh review of all the data you've collected so far, so you can mine what you have for clues.
Start by making a list of all the sources you've found already, even if they have no obvious information that relates to immigration. Then make a timeline of events for your grandfather. Make a note on the timeline next to each event to remind yourself where that information came from. This helps because when you are searching for a person in historical records, whether he will appear in a particular record group depends on knowing the date and the place as well as the name that he was using at that time. You will want to narrow down the window for his arrival as much as possible, in case you have to browse ship passenger lists chronologically instead of searching by name.
The next thing to do is to learn more about the record sets that you plan to search. Use research guides like the ones at Library and Archives Canada, the FamilySearch Wiki, and other sites (see links at the bottom of this answer).
Library and Archives Canada holds microfilmed copies of the passenger lists. Their page Passenger Lists for the Port of Quebec City and Other Ports, 1865-1922 says:
The microfilm copies of the passenger lists from 1865 to 1935 were transferred to LAC by Citizenship and Immigration Canada in four groups: the 1865-1900 records in 1971, the 1900-1908 records in 1980, the 1908-1918 records in 1984, and the 1919-1935 records in 1997. The 1908-1918 portion contains a few lists dated as late as 1921 at the end of the 1918 reels.
Generally speaking, the information which is found on passenger lists for any given period depends on whatever laws were in force at the time the passage was made. Ship companies produced the passenger lists in the departure ports and were used by agents in the arrival ports to process the passengers.
For an example, look at the manifest for a May 1910 arrival of the ship Willehad at FamilySearch. The header on Image 4 reads: "Columns 3, 28, and 30 are to be filled in by the Immigration Agent at the Port of Landing." which suggests that the other columns on the manifest were already filled in before the ship's arrival. The original manifests have been destroyed, but if we had access to the originals instead of these black-and-white film copies, it would be easier to see the different ink colors and handwriting that would show which parts were written at different times.
Working backwards in time from your grandfather's known residence in Canada towards the arrival, try to determine what surname the family used at what time. Names were not changed at the arrival ports by immigration agents, but immigrants did change their names after their arrival in the new country. In the US, correspondence exists between immigrants and the INS where naturalized citizens need to replace their certificate of naturalization and those letters sometimes say what name they were using at the time of their arrival or when they petitioned to be naturalized. It's very likely that if we could see similar correspondence from Citizenship and Immigration Canada, we would see the same kind of content.
Do make a list of all the surname variants you find, and use that to inform your searches. Remember that in most cases, people did not fill out their own records -- the historical records we find like the census were likely dictated to a enumerator, who wrote down the information. What spelling resulted depended on how the enumerator heard the name that was said.
After you have made your review of sources and your timeline, consider other records that you could look for which might have an arrival date on them. Did your grandfather naturalize? His naturalization forms or his national registration forms might help you narrow down his arrival date.
Your grandfather had five sisters -- but you don't say where they were born or when they immigrated. Sometimes we can't find the information we seek about a person in records that were created about them, and we have to look at the records of other family members. Make a timeline for the entire family, and use the census and other records to map out the family's migration pattern.
You don't say what your grandfather's occupation was. In the late 19th and early 20th century, skilled workers were sometimes recruited by industry. Find other people from Romania living in your grandfather's community who worked at similar jobs. Pick someone and use them as a practice or test case to search, in order to become more familiar with the records. You might also be able to find clues by reading general reference books written about Romanian immigrant communities. The more you learn about the big picture, the better you'll be able to pick up clues that will help you find your grandfather.