The (diplomatic) relationship between the Netherlands and Canada became rather strong following the Second World War for two major reasons.

In the first place, Canada sheltered the Dutch royal family from mid-1940 onwards. Queen Wilhelmina, princess Juliana, and princess Beatrix initially fled to the United Kingdom in May of 1940, the Battle of Britain and ensuing Blitz once again gravely compromised the security of the royal family and the Queen's cabinet in London. Queen Wilhelmina opted to stay in the UK, remaining an important figurehead for the Dutch - whether exiled or in the Netherlands. The rest of the royal family were evacuated to Ottawa in Canada, far away from the war's conduct, and essentially in total safety. Princess Juliana - the heir-apparent of Queen Wilhelmina - gave birth to one of her four daughters in Canada. Princess Margriet was born in the Ottawa Civic Hospital, on a ward that for the occassion specifically been designated Dutch sovereign territory, so that Princess Margriet could be born on Dutch soil. Queen Juliana generally experienced her exile in Canada positively, so much so, that upon her return to The Netherlands on May 2nd 1945, she immediately ordered a 100,000 tulip bulbs to be given to Canada, of which some were supposed to grace Ottawa's parks. The choice for the tulip is again twofold. In the first place the tulip is a national flower, that since the 17th century was traded in and grown by the Dutch in significant numbers. Secondly, tulip bulbs were one of the only commodity-like goods that had survived the harsh winter of 1944/45, and the conduct of the war in the country. As a result it's symbolism and availability made it the most feasible of gifts at the time.

Secondly, the war effort in the Netherlands on the ground, was to a major extent conducted by the Canadian First Army. Almost all provinces in the east of the country were liberated the Canadians, who especially in Groningen and Drenthe fought extremely tough urban engagements against German stragglers. Many cities, including Groningen, Zwolle, and Apeldoorn, were quick to recognize Canadian sacrifices, and in the late 1940s established sister-city ties, or had more direct contacts with their liberators. Combined with the gratitude of the royal family, many of these cities either sent tulip bulbs or tulip flowers to show their gratitude. Up until present day, many towns across the (eastern) Netherlands still celebrate their liberation by the Canadians with festivals, that more often than not include elaborate displays of tulips.

SOURCES:

• Antony Beevor's elaborate history of World War II for the bit on the Canadian I Army
• Dutch author and historian Cees Fasseur for the bits on the royal family.
• My own experiences as historian of Dutch national culture with these liberation festivals.

If and when required I would be happy to oblige in the positing of chicago-style references.